Through document WO0204790 pressure pulse generators are known, in which at least two valve bodies are arranged in series in a channel and by being sequentially opened and closed short pressure pulses of pressure fluid are attained which are guided into an actuator cylinder in which a displacable actuator piston is arranged. The actuator piston is in its turn connected to an inlet or outlet valve to a combustion engine. The two adjacent valve bodies are driven by means of one electro magnet each, the activation of which is controlled by a drive unit connected to the combustion engine, which drive unit is provided with software suitable for the application.
A pressure fluid pulse is attained by having the one of the two valve bodies that in the channel in which the valve bodies are located that is located closest to a high pressure source to open while the other valve body is kept in its closed position, whereupon the first valve body is closed and the second valve body is opened. Thereby a pulse of pressure fluid, corresponding to the amount of pressure fluid having high pressure that has been located in the channel between said valve bodies, will be dispatched in the channel in the direction of the actuator piston that is brought into movement. An overlap of the time during which both valve bodies are open for pressure fluid flow can also be used in order to increase the size of the generated pressure pulse.
However, such a construction has the disadvantage that the size of the pulse is decided beforehand in the drive unit and not directly correlates to the wanted displacement of the actuator piston. In order to guarantee that the pulse is not too small, the pulse must be dimensioned such that it is secured that it is big enough for a specific displacement of the actuator piston. Thereby unnecessarily much energy is used for a given displacement of the piston, since a safety marginal is needed.
U.S. Pat. No. 5,193,495 disclose a valve control device comprising an actuator piston that is displacably arranged in a chamber. Furthermore, the disclosed valve control device comprises a first valve that is arranged in a first channel of a pressure fluid circuit, which first channel mouth in said chamber and the first valve is arranged to control the flow of a pressure fluid in this first channel. Thereto, the disclosed valve control device comprises a second valve body that is arranged in a second channel of the pressure fluid circuit, which second channel mouth in said chamber and the second valve is arranged to open and close this second channel. Thus, the first valve and the second valve are not arranged in series in one and the same channel of the pressure fluid circuit.
DK 154165 discloses an actuator comprising an actuator casing having a cylinder and an actuator piston (lower part of the axially displacable “stempel”) displacably arranged in said cylinder. Furthermore, the actuator comprises a pressure fluid circuit having a channel mouthing in said cylinder, an directly electrically controlled first valve body arranged outside the actual actuator casing but still in said channel, and a second valve body (upper part of the axially displacable “stempel”) arranged in the channel. Thereto, the second valve body is fixedly connected to the actuator piston and arranged in series with the first valve body in said channel. The assembled body that constitute the actuator piston and the second valve body has in this context very large mass and is thus inert to accelerate and brake, which bring about restrictions for the useable field of applications of the actuator. Furthermore, the first valve body is directly electrically controlled, and the mass of the first valve body directly affects the opening and closing speed thereof, which is extended by increasing mass.